Slugs - (various species)

Slugs are shell-less mollusks that will feed on ripe strawberries.

Identification

Typical slug.

Jeff Hahn, University of Minnesota

Slugs have fleshy slimy legless bodies that are predominantly different shades of gray. Slugs are basically snails with a reduced shell located internally. Their head contains two pairs of feelers; a larger pair above carries the eyes and a lower pair below is used for smelling. Most slugs in strawberries range in length from 1/4" to 1 1/2".

Important biology

Slugs have a layer of slime to protect their skin from desiccation. As they move, they leave a slime trail which can be used to identify their presence. They prefer moist habitats and locations where they can escape the sun. They feed at night or on dark, overcast days. Slugs lay their translucent eggs under plant debris or in the soil, where the moist conditions provide for optimum development of eggs and young. Continuous straw mulch in a strawberry patch provides such an ideal habitat. Slugs seek out straw mulch and other types of mulch to lay their eggs in the fall and these eggs will hatch in the following spring with the slugs feeding on strawberries in the spring and early summer.

Evidence of slug activity comes in two forms, slug movement and slug feeding. Slugs continually produce slime on which they move and it is a dried slime trail that indicates their travel the previous night.

Slugs have an anatomical structure called the radula which contains small teeth made of chitin. The radula is a rasping organ which scrapes or cuts food before being ingested, and it is the structure that damages the strawberry fruit.

Damage

Slug damage on strawberry.

Ontario Strawberry IPM, OMAFRA

Slugs create varying size holes in the strawberry fruit. The damage can vary from minor practically unnoticeable scraping on the surface of the fruit to significant cavities equal to half of the fruit. When present in large numbers significant damage can be done to the fruit.

Management

Monitoring

Slugs hiding under board.

Jack Kelly Clark, University of California

Slugs should be monitored during and after bloom. In the day look for slime trails in the patch or place wooden boards in the straw underneath which slugs will congregate. Pick up the boards to see monitor slug populations. Keep especially vigilant for slugs during extended periods of overcast and rainy weather. In the evening use a flashlight to check for slugs.

Cultural

Remove potential hiding places for slugs such as weeds vegetation and debris.

Water plants early in the morning to permit all day drying, which avoids creating a moist habitat ideal for slugs.

Place drip irrigation tape close to the plants and avoid creating wet mulch situations which are ideal habitats for slugs.

If you plant in rows keep the width of the rows narrow (12 to 18 in.) to allow quicker drying

Place traps, such as wooden boards and rolled-up newspapers in the patch. Check traps first thing in the morning every day and dispose of the slugs.

Create a slug trap by pouring beer into a shallow pan buried so that the edge is at ground level. Slugs are highly attracted to smells emitted from fermentation processes, and will fall into the pan and drown. Check and renew the trap every couple of days.

Pesticides

Baits need to be considered as a part of a cultural program and employed in conjunction with other methods. Baits alone will not effectively control slugs.

Baits need to be applied prior to the ripening of the berries because the slugs prefer ripe berries to slug bait.

The patch should be irrigated prior to placing the baits to create a situation that will encourage the slugs to be more active. Apply the bait in the late afternoon or evening close to the time when the slugs will begin activity. Sprinkle some bait in protected area where you think the slugs might be hiding such as areas close to walls or fences and in areas which you think the slugs might have to traverse to get to the patch.

Iron Phosphate
Baits that contain iron phosphate don't kill as many slugs as those with metaldehyde, but seem to protect the crop well enough. Iron phosphate baits are cleared for organic production and are safe around children and pets. Baits break down after rains or irrigation. Iron phosphate kills more slowly than metaldehyde and the slugs will seek a hiding place and die there. You may not see slug casualties when you use iron sulfate.